Abstract
Dielectric nanostructures have been widely used to enhance fluorescence intensity, but achieving large-area enhancement of far-field directional fluorescence emission remains a challenge. In this paper, a hybrid structure consisting of a photonic crystal cavity and a grating was designed with the aid of a genetic algorithm to achieve directional and high-ratio emission of near-infrared fluorescence. The resonant wavelength of the photonic crystal cavity was designed to match the excitation and emission wavelengths of fluorescence, while the emission distribution was controlled through the grating to achieve directional emission. The hybrid structure showed remarkable tolerance to the position of fluorescence emitters within the cavity. The emission angle of randomly distributed fluorescence emitters within the cavity was confined in a narrow range of 10°, while average enhancement of fluorescence achieved 120.36 times and the value of fluorescence ratio increases 14.13 times. The hybrid structures represented a viable approach to improve near-infrared ratiometric fluorescence sensing.
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